This invention relates generally to the field of locator systems having multiple individual identity transmitter units and multiple receiver units to receive signals transmitted from the identity transmitter units. More specifically, the invention relates to such systems having data processing means to identify and provide information on the individual identity transmitter units. Even more specifically, the invention relates to such systems where the identity transmitter units send identifying data to the receiver units by infrared (IR) wavelength light pulses.
Systems for locating individual persons or individual equipment within a physical facility such as a hospital or manufacturing plant are known. Early versions, such as taught by Ward in U.S. Pat. No. 3,439,320, utilized ultrasonic transmitters, where each transmitter was tuned to a different frequency. This limited the number of possible identities available to a very small number. Additionally, because the power consumption in the transmitters was high, continual or periodic transmission was not practical and the transmitters were designed to be manually keyed to transmit. Later systems, such as taught by Lester in U.S. Pats. Nos. 3,696,384, 3,729,329, 3,805,227 and 3,805,265, used portable transceiver units which were interrogated by a central transmitter, but these transceivers were very bulky since they had to act as both receivers and transmitters.
It has been discovered that the use of IR transmission is a vast improvement over ultrasonic transmission. IR wavelength light is used for example in remote control devices for operating television or stereo equipment. IR transmission requires less energy, is less susceptible to interference from ambient sources and can be more effectively modulated for data transmission purposes.
One example of an IR transmission and receiver system is taught in U.S. Pat. No. 4,601,064 to Shipley. This is a communication system to automatically establish two-way communication between individual pulse transmitter units and a central controller unit. The individuals carry IR transmitters which transmit automatically and repetitively. Another example is taught by White in U.S. Pat. No. 4,275,385. White's system uses periodic unique IR identification codes emitted from battery powered transmitter units, which are received by overhead mounted IR receiver units. The receiver units also have a unique code, and both are communicated to a central control unit. Both systems use a series of data pulses to create the unique transmitter identities.
The systems referred to above both suffer from a number of drawbacks. The transmitters and receivers of White and Shipley are hard-wired, and as such the identities cannot be changed once a particular unit is built. The transmitted data address is accomplished via amplitude modulation, which requires adjustment of the voltage level. The number of transmitter unit identities is relatively limited, and the range of the receiver units is relatively fixed. The communication between the receiver units and the controller unit is by parallel data through a data and address bus. The receiver units can only store a single identity at any one time.
It is an object of this invention to provide a locator system for personnel and equipment which overcomes the above shortcomings. The system has programmable transmitter units and programmable receiver units. Transmission is via digital pulse modulation with a 16 bit address, and over 65,000 unique identities are available for the transmitter units. Communication between receiver units and the central controller is by serial data stream. The receiver units can store multiple transmitter identities and the range of the receiver units is expandable using slave receivers supplying information to the master receiver unit.